This application is based on and incorporates herein by reference Japanese Patent Application Nos. 2001-384578 filed on Dec. 18, 2001 and 2002-289913 filed on Oct. 2, 2002.
The present invention relates to a distribution type fuel infection pump and, in particular, a load timer which accurately controls fuel injection timing with a deduced hysteresis between an advancing and delaying timings.
A conventional governor that defines performance of a load timer is explained. A governor shaft is provided with an inside way-out whose one end opens to outer circumference thereof and whose the other end communicates with a low fuel pressure side such as a fuel tank. A governor sleeve is provided with an outside way-out which penetrates from an outer surface thereof to an inner surface thereof in sliding contact with the governor shaft. When the governor sleeve advances (in a low load), the inside and outside way-outs communicate with each other. When the governor sleeve backs (in a high load), the communication between both the way-outs are shut off. The above conventional load timer has a characteristic that injection timing is retarded as the pump chamber is depressurized in the low load, as shown in FIG. 2B, and the injection timing is advanced as the pump chamber is pressurized in the high load.
Further, there is known a load timer that has a different characteristic. When the governor sleeve advances (in a low load), the communication between the inside and outside way-outs is shut off so that the pump chamber can be pressurized. When the governor sleeve backs (in a high load), both the way-outs communicate with each other so that the chamber can be depressurized. This structure provides an inverse advancing and retarding characteristic as shown by a solid line A and a dotted line J in FIG. 2A. This characteristic improves an ignition characteristic by advancing injection timing in the low load and upgrades an exhaust characteristic by retarding the injection timing in the middle and high load. This inverse advancing and retarding characteristic is disclosed in JP-U-H4-1644.
Recently a social background has involved a stringent emission limit of a diesel engine, so a highly accurate fuel injection pump is desired. However, a fuel injection pump that has the inverse advancing and retarding characteristic (inverse characteristic load timer) exhibits a hysteresis between a retarding characteristic while the load increases (dotted line J shown in FIG. 2A) and an advancing characteristic while the load decreases (solid line B shown in FIG. 2A) . This hysteresis adversely affects on a highly accurate advancing and retarding control (injection timing control).
It is an object of the present invention to provide a distribution type fuel injection pump in which an accuracy of fuel injection timing is enhanced by decreasing a hysteresis between a retarding characteristic while a load increases and an advancing characteristic while the load decreases.
To achieve the above and other objects, a distribution type fuel injection pump is provided with a governor as follows: The governor includes a governor shaft and a governor sleeve. An inner surface of the governor sleeve is slidably fitted to an outer circumference of the governor shaft. An inside way-out is provided in the governor shaft and includes a first shaft port, a second shaft port and an annular groove. The first shaft port is axially formed in a center of the governor shaft, and one end of the first shaft port communicates with a suction side of the pump, while the other end of the first shaft port is sealed. The annular groove formed in the outer circumference of the governor shaft faces the inner surface of the governor sleeve. The second shaft port extends in a radial direction of the governor shaft across the first shaft port and an inlet of the second shaft port opens to a bottom of the annular groove. An outside way-out is provided in the governor sleeve. One end of the outside way-out opens in the inner surface of the governor sleeve and faces the outer circumference of the governor shaft. And the other end of the outside way-out communicates with the pump chamber. When the governor sleeve advances, the communication between the inside and outside way-outs is shut off and the communication between the suction side of the pump and the pump chamber is shut off. The fuel pressure in the pump chamber is thereby increased. When the governor sleeve backs, both the way-outs communicate with each other and both of the suction side of the pump and the pump chamber are communicated with each other. The fuel pressure in the pump chamber is thereby decreased. And one of a chamfering portion formed by cutting off flatly a corner and a rounding portion formed by rounding a corner is provided in the inlet of the second shaft port that opens to the bottom of the annular groove.
The above chamfering/rounding portion in the inlet of the second shaft port of the inside way-out decreases energy loss caused by fuel flowing into the inside way-out and improves a flow characteristic of the fuel. This improvement restrains a hysteresis between pump chamber pressure decrease while the load increases and pump chamber pressure increase while the load decreases. This thereby results in lowering a hysteresis between a retarding characteristic while the load increases and an advancing characteristic while the load decreases, and securing a highly accurate fuel infection timing control.